Gear box mechanisms sometimes require an isolation or damping system to minimize transmission of operating vibration or noise. An example is in the case of underwater craft, such as torpedoes are prone to radiate noise to the surrounding water. Various approaches have been taken to isolate or reduce noise from machinery, engines, transmissions or the like, including noise from the hull area of a torpedo. Compliant gears or vibration damping composite structures have been used.
For instance, compliant gears having elastomer layers or composites within the gear structure itself have been proposed for isolating noise from the meshing gears, such as in U.S. Pat. No. 2,460,629 to Fawick. A problem in using compliant gears is that the elastomers or other elastic materials undergo stress just like the gears themselves, and therefore must be fabricated accordingly. Copending application Ser. No. 944,926, filed Dec. 22, 1986, and assigned to the assignee of this invention, addresses the noise radiating problem by providing a novel composite wall structure designed to reduce low frequency vibrations as well as to dampen resonant vibrations. Such a composite wall structure, while being quite effective for its intended purpose, may be too expensive for some applications.
Copending application Ser. No. 087,653, filed Aug. 20, 1987, and assigned to the assignee of this invention, provides a vibration isolating mounting system for the gearbox itself, by providing a two-stage vibration mount between an inner housing structure and an outer housing structure, as well as between the outer housing structure and an appropriate supporting frame means.
The present invention addresses the problem of vibration or noise damping or isolation by providing a novel bearing means between a housing structure and an inner rotatable component, such as an output gear, the bearing means itself providing for noise damping.